Metal molybdite catalyzed decarbonylation of furfural to furan



Patented Apr. 7, 1 953 UNITED STATES PATENT OFFICE METAL MOLYBDITECATALYZED DECAR- BONYLATION F FURFURAL TO FURAN James E. Carnahan, NewCastle, Del., assignor to E. I. du Pont de Nemours and Company,Wilmington, DeL, a corporation of Delaware No Drawing. Application April17, 1951, Serial No. 221,533

furan from furfural in good yields and with minimum of side-reactionproducts. will appear hereinafter.

The'objects of this invention are accomplished by the following processfor decarbonylating furfural to furan which comprises contactingfurfural and water with a non-ferrous metal molyb- Other objects 'diteor-a mixture of molybdites of ferrous metals whose ions are solubleinaqueous ammonia in amount greater than that stoichiometricallyrequired to precipitate the metal ion. This invention provides a new anduseful process for obtaining furan from furfural, which compriseseffecting the decarbonylation of furfural in the presence of anon-ferrous metal molybdite, particularly a zinc or copper molybdita'orin the presence of a mixture of molybdites of ferrous metals whose ionsare not precipitated as insoluble oxides or hydroxides when solutions oftheir salts are treated with excess aqueous ammonia. Such a mixture offerrous metal molybdites is a mixture of nickel and cobalt molybdites.

In one embodiment of this invention, a catalyst chamber is charged withthe molybdite catalyst and the catalyst heated to between 350 and 500 C.A vapor mixture of water and furaldehyde (furfural), in the ratio of atleast 5 moles of water per mole of furaldehyde, is then passed overtheheated catalyst at a velocity corresponding to between 2 and 500gram-moles of va or per liter of catalyst per hour. The products ofreaction are collected in suitable traps and the collected product isthen subjected to fractional distillation, or other means known to thoseskilled in the art, to isolate the desired product.

The examples which follow are submitted to illustrate and not to limitthis invention.

Example I A stationary-bed tubular reactor was charged with 95 ml. (131g.) of copper molybdite catalyst prepared in 8:14 mesh granular formaccordin to directions given subsequently. Furfural (96 g.,

gas. The calculated vapor space velocity was 860 hr.- and apparentcontact time was 1.5 seconds. The effluent products were condensed inappropriate cold traps and separated by fractional distillation. Furanwas obtained in 25% conversion and 43% yield. Unconverted furfural wasrecycled.

Emample II Example I was repeated except that zinc molybdite ml., 143g.) was employed as catalyst, and the process was conducted at 4.40:10C. during 3.0 hours. The calculated vapor space velocity was 1140 hr:and the apparent contact time was 1.2 seconds. Furan was isolated in 18%conversion and 32% yield.

The examples have illustrated certain preferred embodiments of theinvention. It is to be understood that variation therefrom may be hadwithout departing from the scope or spirit thereof.

The catalysts used in the practice of this invention are the metalmolybdites described in the copending application of H. R. Arnold and J.E. Carnahan, U. S. Serial No. 111,982 filed August23, 1949, now D. S.Patent No. 2,572,309, issued October 23, 1951. These molybdites exist intwo series, in the first of which the molybdenum is present in thequadrivalent state corresponding to the oxide M002, and the hypotheticalacid HzMOOa, and in the second the molybdenum exists in the bivalentstate corresponding to the oxide M00 and the hypothetical acidH2MoO2.Thus, zinc molybdite has the formula ZIIMOOs and copper molybdite hasthe formulas CllMOOz and CuMoOs.

if desired, and they may be employed in'the form of pellets or as finelydivided powders. They may be used as such or extended on inert supportssuch as charcoal, alumina, silica, etc.,-or they may be mixed withmetallic pellets, such as copper, iron, etc., pellets. The latterconstitutes a particularly preferred form of using the catalysts becausethe pellets act as heat-dissipating media and in that way make itpossible to exercise better temperature control on the reaction. Theparticular form of the catalyst for maximum activity depends upon theconditions under which the decarbonylation reaction is to be effected.Thus, for vapor or liquid phase continuous operation it is best to havethe catalyst in the form of pellets, especially pellets mixed with metalturnings or pellets.

A typical preparation of copper molybdite usefully employable in thepractice of this invention is the following:

Seventeen hundred sixty-six grams of ammonium paramolybdate,(NI-I4)eMo7O24.4H2O, equivalent to 10 moles of M003, was dissolved in5000 cc. of distilled water and neutralized by the addition of 900 cc.of 28% aqueous ammonia. The resulting solution of ammonium molybdate(NH02M0O4 containing 1.9 moles excess ammonia was added with stirring,at room temperature, to a solution of cupric nitrate prepared bydissolving 2416 grams of cupric nitrate trihydrate, Cu(NO3)2.3H20,equivalent to 10 moles of the cupric salt, in 5000 cc. ofdistilled"water."'-'A pale green precipitate was formed in an acidslurry having a pH of approximately 3.9.. The pH of the slurry wasadjusted to '7 (Beckman pH :meter) by the1additionof;630 cc. of 28%aqueous ammonia. The precipitate was then washed, filtered; dried, andcalcined at 400 C. for 24 hours. Analysis of the calcined product showedit to contain 29.7% copper and 37.7% molybdenum. The "calcined-productwas reduced in 80 N2/20 H2 gas mixture at gradually increasingtemperature up to 450 C. for a total of 26 hours, of which about 20hours was at 450 C. The reduced product was pyrophoric on exposure toair. Analysis of the reduced material showed it to contain 34.45% copperand 49:10% molybdenum; corresponding closely to CuMoOz. r

Inplace' of zinc andcopper molybdites there can be used mixtures ofmolybdites of ferrous metals whose ions are soluble in aqueous ammoniain amount greater thanthat required to precipitate themetal ion.Examples of such mixtures or ferrous group metal molybdites arenickeland cob'alt'molybdites. These are much less preferred because ofthe efficiency of the decarbonylation reaction is much lower than it iswitlithe aforementioned non-ferrous group metal molybdites.

Y The amount of catalystemploy'ed depends upon such interdependentvariables as temperature, pressure, mode of operation, feed rate, etc.In general the amount of catalyst usedis that required to bring aboutreac'tion'at a suitable rate under the conditions used. In a batchoperation the amount will vary from about 0.01 to about 20% by weight offurfuial being decarbonylated. In" continuous operation the" weight of'furfural decarboriylated'at any given instant is less than the weightof catalyst, but the total weight of ,furfural -which may bedecarbonylated' during 'theac'tive life of the catalyst is at least 10times the catalyst weight.

The'decarbonylation process of this invention 'is carried out'at'ordinary atmospheric pressure andthis has a marked practicaladvantage from the standpoint of ease f operation, simplicity 'ofequipment requirements, etc. If desired, ho'weverjthe process can beoperated at subatmos ph'eric pressure orlat superatmospheric pressuresof 'up to 100 or more pounds per square inch. I As a rule the processis'carried out at temperaturesof froin 350 to 500 C/Sirlce the bestyields of. desired products are obtained in the rangeof-40oi to 475C.,.this embraces the pre- I ferredLtemperature conditions.

' Although the decarbonylationreaction can be efiected by contacting thefurfural alone with the catalyst, usually better results from thestandpoint of yield of desired product and life of the catalyst areobtained by employing water in conjunction with the furfural. Goodresults are obtained using as little as one mole ofwater per mole offurfural but better yields, with greater freedom from side reactionproducts, result if the amount of water is at least 5 moles per mole offurfural. If desired, an inert diluent gas such as nitrogen can beemployed in conjunction with thefurfural.

' Feed-rate is an important variable since it determines the amount ofiurfural which can be processed in aunit of time through a unit volumeof catalyst per hour. As a rule the feed-rate will .vary from 2 to 500gram-moles of vapor per liter of catalyst per hour. The best results areobtained using a feed-rate of from 20 to 70 grammoles of vapor perliter'of catalyst per hour and this constitutes a preferred condition.

The decarbonylation process of this invention makes possibletheobtainment of iuran from furfuralin good yields and withminimum ofsidereaction products, which minimizes isolation and purificationproblems.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

Iclaim:

l. A process for decarbonylating furfural to furan which comprisescontacting a mixture of furfural and water with a catalyst heated to atemperature of 350 to 500 C. and which is selected from the classconsisting of non-ferrous metal molybdites and mixtures of molybdites offerrous metals whose ions are soluble in aqueous ammonia in amountgreater than that stoichiometrically required to precipitate the metalion.

2. A process for decarbonylating furfural to furan. which comprisescontacting-a mixture of furfural and water with a non-ferrous metalmolybdite heated to a temperature of 350 to 3. A process fordecarbonylating furiural to furan which comprises contacting a mixtureof iurfural and water with zinc molybdite heated to a temperature of 350to 500 C.

4. A process for decarbonylating furfural'to furan which'comprisescontactinga mixture of furfural and water with copper molybdite heatedto a temperature of,350 to 500 C.

' JAMES E. CARNAHAN.'

REFERENCES CITED The following references are of record in the 'file ofthis patent:

UNITED STATES PATENTS Great Britain Feb. 14, 1946

1. A PROCES FOR DECARBONYLATING FURTURAL TO FURAN WHICH COMPRISESCONTACTING A MIXTURE OF FURFURAL AND WATER WITH A CATALYST HEATED TO ATEMPERATURE OF 350 TO 500* C. AND WHICH IS SELECTED FROM THE CLASCONSISTING OF NON-FERROUS METAL MOLYBDITES AND MIXTURES OF MOLYBDITES OFFERROUS METALS WHOSE IONS ARE SOLUBLE IN AQUEOUS AMMONIA IN AMOUNTGREATER THAN THAT STOICHIOMETRICALLY REQUIRED TO PRECIPITATE THE METALION.